In mixing of video signals to produce one edited video signal from two or more video signal sources, a method known as non-additive mixing (NAM) is sometimes adopted. An explanation will be made of non-additive mixing of video signals below.
In non-additive mixing, comparison is made to the values of the luminance signals Y of for example two video signals each containing component signals, for example, a luminance signal Y and two color difference signals U and V or a luminance signal Y and two color difference signals P.sub.B and P.sub.R, selection is made of the video signal having a luminance signal Y with the larger value. This is typically called a positive NAM. Conversely, there is known a method of selectively outputting the video signal giving a luminance signal Y with a smaller value and mixing the video signals. This is called as a negative NAM.
In the NAM processing of video signals, when two video signals to be mixed have a predetermined relationship, for example, when the values of the luminance signals Y of the two video signals are substantially the same, noise occurs in at least one of these luminance signals, and the color difference signals U and V (hue) of the two video signals are considerably different from each other, it suffers from the disadvantage that the resulting or deteriorated video signal is unnatural. This phenomenon typically derives from the fact that the relative magnitudes of the values of the luminance signals Y of each of the two video signals end up irregularly mixed by noise and, along with this, the other signal components, that is, the considerably mutually different color difference signals U and V of the two video signals also end up irregularly switched. The picture resulting from video signals where these two video signals are irregularly mixed ends up with noise occurring at part or all of the picture.